Nuclei Of Mass Number Research Articles

Overall picture of the cascade gamma decay of neutron resonances within a modified practical model

The intensities of two-step cascades in 43 nuclei of mass number in the range of 28 ≤ A ≤ 200 were approximated to a high degree of precision within a modified version of the practical cascade-gammadecay model introduced earlier. In this version, the rate of the decrease in the model-dependent density of vibrational levels has the same value for any Cooper pair undergoing breakdown. The most probable values of radiative strength functions both for E1 and for M1 transitions are determined by using one or two peaks against a smooth model dependence on the gamma-transition energy. The statement that the thresholds for the breaking of Cooper pairs are higher for spherical than for deformed nuclei is a basic result of the respective analysis. The parameters of the cascade-decay process are now determined to a precision that makes it possible to observe the systematic distinctions between them for nuclei characterized by different parities of neutrons and protons.

Energy dependence and systematics of level-density parameters in nuclei of mass number in the range of A = 20–60

Existing direct and indirect experimental data on level densities in excited nuclei of mass and charge number in the ranges of A = 20–60 and Z = 11–27, respectively, were compiled and analyzed. Contradictions between values extracted from the results of measurements performed by different methods were revealed. Consistent input data were selected, and a systematics of level-density parameters was created on this basis within the generalized model of superfluid nuclei. The effect of the first discrete vibrational levels on extracted parameters was studied.

Dispersive optical potential for nuclei with N and Z values changing toward the nucleon drip lines

A method for constructing dispersive optical potentials is proposed for calculating single-particle energies in isotopic chains of spherical and nearly spherical nuclei up to nucleon drip lines. The potential of this method is demonstrated by calculating the neutron and proton single-particle energies in calcium, nickel, and zirconium isotopes. The results agree well with experimental data available for stable isotopes. Predictive calculations of single-particle spectra are performed for isotopes lying far from the beta-stability valley. A comparison of the results with the energies of nucleon separation from nuclei of mass number A and A+1 revealed features of the single-particle spectrum that are characteristic of nuclei containing classical and nonclassical magic numbers of nucleons.

Decay of giant resonances in light and medium-mass nuclei from coincidence experiments with charged particles

In recent years, the physics of electromagnetic interactions has made considerable advances in studying giant multipole resonances, which are highly excited collective states of nuclei. After the advent of new-generation continuous-beam accelerators, (e, e′x) coincidence experiments were performed, and new precision data on giant multipole resonances were obtained from these experiments. A number of examples of cross sections for decay accompanied by proton and alpha-particle emission in p-, sd-, and pf-shell nuclei of mass number in the range 16 ⩽ A ⩽ 64 are given. The relative contributions of these reactions are compared, their general and special features are revealed, and evaluations for semidirect and statistical decays are presented.

Isospin symmetry and giant resonance in nuclei of mass number A = 14

An analysis of the cross sections for photon absorption by isobar nuclei 14C and 14N in the giant-dipole-resonance region demonstrates a high degree of isospin symmetry for this type of collective excitations in the above nuclei. Giant resonances in A = 14 isobar nuclei are related by a simple rescaling procedure that is based on the fact that, for these nuclei, the isospin remains a good quantum number in the process of dipole excitations of energy up to about 40 MeV. The features of the isospin splitting of the giant resonance in the 14C nucleus are refined. The shape of the cross section for photoabsorption in the 14C nucleus—in particular, a large width of the giant resonance in this nucleus—is exhaustively explained.

Nuclear magnetic moment of the143Ceground state

The nuclear magnetic moment of the ${}^{143}\mathrm{Ce}$ ground state ${(T}_{1/2}=33.0 \mathrm{h},{I}^{\ensuremath{\pi}}{=3/2}^{\ensuremath{-}})$ has been measured with the technique of nuclear magnetic resonance on oriented nuclei (NMR-ON) at low temperature. A sample ${(}^{143}\mathrm{Ce}Fe)$ was prepared by implanting into an Fe foil nuclei of mass number 143, which were separated from fission products with an on-line isotope separator. The NMR-ON spectra were obtained by detecting specific $\ensuremath{\beta}$ and $\ensuremath{\gamma}$ rays, and the resonance frequency was thereby determined to be 84.3(1) MHz. Using the reported value of the hyperfine magnetic field at other Ce nuclei in Fe, the nuclear magnetic moment of the ${}^{143}\mathrm{Ce}$ ground state was determined to be $|\ensuremath{\mu}|=0.43(1) {\ensuremath{\mu}}_{N}.$ This value is discussed based on a systematics of the magnetic moments of other $N=85$ nuclei.

The Sp(3, [formula omitted]) representations of an A-particle nucleus

An interactive program to evaluate the symplectic representations associated with a nucleus of mass number A. The code is in C language and is based on an algorithm developed by one of the authors (MJC). This code is mainly of interest to the implementation of the nuclear symplectic shell model. However, with appropriate (tedious but straightforward) modifications it can be used to evaluate the so-called ‘discrete (D +) series’ unirreps of Sp( n, R ), for arbitrary n.

A simple description of nucleon high-momentum components due to short-range correlations in nuclei

Effects of short-range correlations are included in nuclear momentum distribution also using a simple method suitable for high mass number nuclei.

Nucleon Effective Mass and theADependence of Structure Functions

The nucleon effective mass was successfully used, as the only free parameter, to adjust the ratio R(A) of structure functions measured in a nucleus of mass number A and in the deuteron, for each A value in the SLAC set of experimental data. The resulting A dependence of the effective mass, being linear in A/sup -1/3/, is consistent with the behavior expected from nuclear structure considerations. The extrapolated value of the effective mass for nuclear matter agrees with previous estimations.

Statistical fluctuations of (d, p) and (d, α) reactions on32S target nuclei at 135°

The auto-correlation analysis of the fluctuations of the differential cross-sections of the (d, p) and (d, α) reactions on32S target at 135° gave a mean level width “Γ” of 20±5 keV for the34Cl compound nucleus at 13.630 MeV average excitation energy. This value of “Γ” eflects the nuclear shell structure ef fects for even mass number nuclei beside confirming the rermigas model predictions. The absence of correlation between associated as well as between Fon-associated decay groups is confirmed. The validity of the Thomas-Porter distribution for nescribing the probability distribution of cross-sections around their averages is attributed do a very small contribution of the direct process to the reaction mechanism if present. The tprobability of the α-isospin forbidden transition to the30P first excited state is discussed in the frame of the isospin mixing.

Effective interaction calculations for nuclei of mass 6 to 9

Shell model calculations using the effective interaction approach of Talmi are reported for normal parity states in nuclei of mass number 6–9. To fit simultaneously the energies of levels in these nuclei, energy shifts of ground state rotational bands in 8 Be and 9 Be are introduced. These shifts have their origin in the deformations of nuclei. The obtained matrix elements fit the data better than those of earlier authors, and resemble the matrix elements obtained from realistic interactions such as the Hamada-Johnston potential. Theoretical predictions are compared with new experimental data. M1 radiative widths, log ft values, and spectroscopic factors for single- and two-nucleon transfers are given to help in the interpretation of new data. The need for carrying out more calculations for 1p shell nuclei with realistic forces is discussed.

Nuclear data sheets for A = 169

The available nuclear structure information is presented for all nuclei of mass number A = 169. Experimental data are evaluated for these deformed nuclei. Arguments for spin and parity assignments are given for many excited states. Levels are interpreted either as Nilsson states or as vibrational excitations with associated rotational bands. Compilers have checked for inconsistencies in branching ratio and conversion coefficient data from decay and reaction experiments, where comparison can be made.

The URCA process at high temperatures and densities

The URCA neutrino loss rate from a hot stellar environment is investigated. The results indicate that the loss rates for URCA type processes from even mass number nuclei are comparable to the rates from odd mass number nuclei at temperatures above about 109 K. Rates are calculated for some typical odd mass isobar pairs and for the even mass isobar fifty-six for temperatures between 5×108 K to 5×1010 K.

Holes in the 1p shell in the unified model

The negative parity levels in nuclei of mass number A = 13, 17, 19 are derived on the basis of a hole in the 1p32or 1p12 shells weakly coupled to the surface oscillations.

Note on the Spins of Nuclei of Mass Number Ten

Note on the Spins of Nuclei of Mass Number Ten